Erasable optical disk and optical information recording/reproduction apparatus

ABSTRACT

This invention provides an erasable optical disk, on which information is recorded and reproduced repeatedly through the irradiation of laser beams, and an optical information recording/reproduction apparatus which records and reproduces information on the erasable optical disk. In erasing and then recording information on the erasable optical disk by using an erasing laser beam and a recording/reproduction laser beam, respectively, the tracking of both laser beams on the same track is detected so as to prevent erroneous erasing. The apparatus uses the optical disk having a mark signal disposed between a sector identifier and a data field, which mark signal is capable of determining the presence of the erasing laser beam on an adjacent track on the erasable optical disk, and the apparatus reproduces and detects the mark signal by using the erasing laser beam. The apparatus discriminates the position of the erasing laser beam depending on whether the mark signal has been detected or not, thereby preventing erroneous erasing of data on the adjacent track and simultaneously assuring the presence of the erasing laser beam on the same track along with the recording/reproduction laser beam.

This application is a continuation of application Ser. No. 07/471,780,filed Jan. 29, 1990 (now abandoned) which in turn was a division ofapplication Ser. No. 159,743 filed Feb. 24, 1988 (which issued as U.S.Pat. No. 4,939,713).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical disk and optical informationrecording/reproduction apparatus, and particularly to an erasableoptical disk on which information is recorded, reproduced and erasedrepeatedly through irradiation of a laser beam, and to an opticalinformation recording/reproduction apparatus which records andreproduces information on the erasable optical disk.

2. Description of the Related Art

FIG. 8 shows, as an example, the phase transition between thenoncrystalline state (A) and the crystalline state (C) of a phasevarying recording medium on a conventional optical disk. The recordingmedium records a signal by a variation between the noncrystalline state(A) of a small reflectivity and the crystalline state (C) of a largereflectivity. A signal is recorded in such a way that a portion of therecording medium in the crystalline state (C) having a largereflectivity is heated locally to a temperature near the fusing pointand then cooled quickly to bring it into the noncrystalline state (A)having a small reflectivity. The recorded signal is erased by heatingthe recording medium to a temperature near the fusing point and thencooling it slowly so that the portion irradiated by the laser beam isbrought into the crystalline state (C) having a large reflectivity.

FIGS. 9A and 9B are diagrams illustrating the principle of signalrecording and erasing by using a recording/reproduction laser beam andan erasing laser beam. FIG. 9A shows the spot shape of laser beams forrealizing the heating and rapid cooling condition and the heating andslow cooling condition for the recording medium. FIG. 9B shows therespective laser intensity distributions. In these figures, indicated by23 is a spot of a recording/reproduction laser beam of a shortlongitudinal length of the order of 1 μm, 23a is its laser intensitydistribution, 24 is a spot of an erasing laser beam of a longlongitudinal length in the range from several μm to ten-odd μm, and 24ais its laser intensity distribution. Indicated by 25 is a guide track onwhich the recording medium is deposited by evaporation. Depending on thedifferences in the laser spot longitudinal length and intensitydistribution, the two distinct heating and cooling conditions aredetermined, i.e., the short longitudinal length beam spot determines theheating and rapid cooling condition, and the long longitudinal lengthbeam spot determines the heating and slow cooling condition.

In operation, the erasing laser beam 24, which precedes therecording/reproduction laser beam 23 irradiates the information sectionon the guide track 25 with a constant intensity so that an old signalrecorded in the information section is erased and then the followingrecording/reproduction laser beam 23 records a new signal in theinformation section.

With the above-mentioned structure, however, it is necessary that therecording/reproduction laser beam 23 and the erasing laser beam 24 arepositioned on the same guide track 25. In a two-beam optical informationrecording/reproducing apparatus generally in use, two separatesemiconductor laser sources are used to produce two respective laserbeams 23 and 24 which are arranged as shown in FIG. 9A. Hence, it isdifficult to maintain both laser beam spots 23 and 24 positioned on thesame guide track only by the precision of mechanical structure.Accordingly, it becomes necessary to apply tracking servo control to theerasing laser beam 24 in the same way as the recording/reproductionlaser beam 23. However, even when the tracking servo control is appliedto the erasing laser beam 24, the tracking actuator provides a movablerange of 2-3 μm in the disk radial direction. Therefore, even when thetracking servo system is in operation, it is not guaranteed that theerasing laser beam 24 tracks the same guide track 25 in the same way asthe recording/reproduction laser beam 23. On this account, there hasbeen a problem that the erasing laser beam erroneously erases the recordon an adjacent track. Besides, the same problem has been the case wherethe laser beam brings about track jump due to the vibration or shock.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide an opticaldisk and optical information recording/reproduction apparatus capable ofdetecting and assuring that the recording/reproduction light beam andthe erasing light beam are positioned on the same guide track andcausing the erasing and recording operation to be stopped immediatelywhen it is determined that both beams are not on the same track.

This invention relates to an optical disk having a sector identifierwhich records sector address information, a data field in whichinformation is recorded and a mark signal disposed between the sectoridentifier and the data field for identifying that the erasing lightbeam is positioned on an adjacent track, and also relates to an opticalinformation recording/reproduction apparatus comprising means forsequentially projecting an erasing light beam and arecording/reproduction light beam, recording and reproducing means forrecording and reproducing information by using therecording/reproduction light beam, erasing means for erasing recordedinformation by using the erasing light beam, and mark signal detectingmeans for reproducing and detecting a mark signal by using the erasingbeam.

With the optical disk of this invention, it is possible to detect themark signal by using the erasing light beam and to determine that theerasing light beam is positioned on the same track along with therecording/reproduction light beam, and with the optical informationrecording/reproduction apparatus of this invention, it is possible todetermine the position of the erasing light beam according to thedetection or nondetection of the mark signal by the mark signaldetecting means whereby it is made possible to prevent erroneous erasureof data on an adjacent track and to guarantee that the erasing lightbeam and the recording/reproduction light beam are positioned on thesame track.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing the sector format of the opticaldisk embodying the present invention;

FIGS. 2A, 2B and 2C are diagrams illustrating an embodiment of the marksignals M1 and M2 shown in FIGS. 1A and 1B;

FIG. 3 is a block diagram showing the first embodiment of the opticalinformation recording/reproduction apparatus using the optical disk ofthe present invention;

FIG. 4 is a waveform diagram showing the waveform of the signals intoand from the various blocks in FIG. 3;

FIG. 5 is a block diagram showing the second embodiment of the opticalinformation recording/reproduction apparatus using the optical disk ofthe present invention;

FIG. 6 is a block diagram showing the third embodiment of the opticalinformation recording/reproduction apparatus;

FIG. 7 is a waveform diagram showing the waveform of the signals intoand from the various blocks in FIG. 6;

FIG. 8 is a diagram illustrating the phase variation between thenoncrystalline state (A) and the crystalline state (C) of a phasevarying recording medium; and

FIGS. 9A and 9B are diagrams illustrating the principle of erasing andrecording of information.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows the sector format for odd-numbered track addresses, andFIG. 1B shows the sector format for even-numbered track addresses. Inthe figures, indicated by ID is a sector identifier which is a record ofsector address information, DF denotes a data field in which data isrecorded, M1 and M2 are mark signals indicative of an even or odd trackaddress as detected by an erasing beam, G11 and G12 are gaps havingrespective different lengths T1 and T2 for identifying the mark signalsM1 and M2, and G21, G22 and G3 are gaps for absorbing a transientresponse time of the laser beam output and a variation of the diskrotational speed.

FIGS. 2A, 2B and 2C show the concrete structure of the mark signals M1and M2 shown in FIG. 1. FIG. 2A is a diagram showing the intensity ofthe laser beam reflected from the track, FIG. 2B is a plan view of pitsand grooves which give rise to changes in the reflected laser intensityas shown in FIG. 2A, and FIG. 2C is a perspective view of the track. Thesector identifier ID is formed in the shape of pits having a constantdepth, whereby address information is modulated and recorded. The marksignals M1 and M2 are flat land portions intervening between the groovesas shown in FIG. 2C, each having a length in the range from several μmto ten-odd μm detectable by the erasing beam. The mark signals aredetected through a phase variation of the laser beam caused by thegroove depth. The mark signals M1 and M2 have their land portionsarranged in accordance with the track number, even or odd, as shown inFIG. 2C, and they are discriminated and detected by a difference in theamount of the laser beam reflected from the groove and flat portions.The data signal is recorded in the data field DF by the variable densitytype recording in which a laser beam is controlled to irradiate grooves,where a recording film is deposited by evaporation, so that acrystalline state thereof is changed to an amorphous state thereby tocause the reflectivity to be changed.

In order to effect the optical recording using the above-mentionedsector format, the optical head is designed to have mechanical precisionso that the erasing light beam does not cause a track offset in excessof ±1 track. This allowance of ±1 track offset is considered to be areasonable condition from a practical point of view.

In the case where the recording/reproduction light beam 23 is trackingan odd-numbered track shown in FIG. 1A, if the erasing light beam 24 ispositioned on an even-numbered track shown in FIG. 1B, a reproductionsignal produced by the erasing light beam 24 causes the mark signal M2to be detected, while, if the erasing light beam 24 is positioned on anodd-numbered track, the mark signal M1 is detected. On the other hand,in the case where the recording/reproduction light beam 23 is trackingan even-numbered track, if the erasing light beam 24 is tracking thesame even-numbered track, the erasing light beam 24 causes the marksignal M2 to be detected, while, if the erasing light beam 24 ispositioned on an odd-numbered track, it causes the mark signal M1 to bedetected. Accordingly, by detecting the mark signal M1 or M2 with theerasing light beam 24, on-tracking or off-tracking of the erasing lightbeam 24 can be determined.

In the example of FIGS. 2A, 2B and 2C, the data field is recorded in agroove. Alternatively, if the data field is recorded on a land, the marksignals M1 and M2 are formed as grooves.

FIG. 3 is a block diagram showing a first embodiment of the opticalinformation recording/reproduction apparatus using the optical disk ofthis invention. In the figure, indicated by 1 is an address reproductioncircuit which reads out a track address and a sector address from theID, 2 is an M1 gate signal generation circuit for producing a gatesignal 104 for gating the mark signal M1, 3 is an M2 gate generationcircuit for producing a gate signal 105 for gating the mark signal M2, 4is an inverter, 5 and 6 are 3-input AND gates, 7 is a 2-input OR gate, 8is a sector control circuit which generates a gate signal for erasing orrecording data in an addressed sector, 9 is a comparator for convertingan analog signal into a binary signal, 10 is a differentiation circuitfor detecting a rising edge of a signal, 11 is a set-reset flip-flop, 12is a 2-input AND gate, 13 is an erasing laser drive circuit, 14 is adata modulation circuit which produces write data 114 obtained by addinga clock resynchronizing pattern, a data section start mark, etc. to adigitally modulated signal obtained by digitally modulating data towhich an error correction code has been added, 15 is arecording/reproduction laser drive circuit, 16 is an erasing lasersource, 17 is a recording/reproduction laser source, 100 is a signalreproduced from the optical disk by a recording/reproduction light beam23 emitted from the recording/reproduction laser source 17, 101 is asignal reproduced from the optical disk by an erasing light beam 24emitted from the erasing laser source 16, 102 is a binary representationof a signal reproduced by the erasing light beam 24, 103 is an addressdetection signal indicating that an address has been read out, 104 is anM1 gate signal for gating the mark signal M1, 105 is an M2 gate signalfor gating the mark signal M2, 106 is an address odd/even signalindicating whether an associated track address is even or odd, 107 is atracking deviation detection signal indicating the tracking deviation oraberrance of an erasing beam, 108 is an address data signal, 109 arecommand signals for erasing recording, reading and the like 110 is anerasing gate signal for activating the erasing laser source 16, 111 is amodulation start signal, 112 is an enabling signal for activating theerasing laser drive circuit 13, 113 is a write gate signal indicatingthe validity of the write data 114 recorded in the data field, and 114is the write data.

FIG. 4 shows signal waveforms appearing at various portions of theoptical information recording/reproduction apparatus shown in FIG. 3.Shown in FIG. 4(a) is the positional relationship between the respectivelight spots of the recording/reproduction light beam 23 and the erasinglight beam 24. In FIG. 4, waveforms shown by solid lines denote a casewhere the recording/reproduction light beam 23 is positioned on a trackof an odd-numbered address as shown in FIG. 4(b) and the erasing lightbeam 24 is positioned on a track of an even-numbered address as shown inFIG. 4(c). While, waveforms shown by broken lines denote a case wherethe recording/reproduction light beam 23 is positioned on a track of aneven-numbered address as shown in FIG. 4(c) and the erasing light beam24 is positioned on a track of an odd-numbered address as shown in FIG.4(b). The recording/reproduction light beam 23 and the erasing lightbeam 24 are apart from each other by time t as shown in FIG. 4(a).Therefore, the reproduced signal 101 by the erasing light beam 24 shownin FIG. 4(e) precedes the reproduced signal 100 by therecording/reproduction light beam 23 shown in FIG. 4(d) by time t.

The following describes the operation of the optical informationrecording/reproduction apparatus according to the first embodiment ofthis invention having the construction as described above. The operationis based on the assumption that the recording/reproduction light beam 23is positioned on a track of an odd-numbered address as shown in FIG.4(b) and the erasing light beam 24 now under tracking deviation oraberrance is positioned on a track of an even-numbered address.

The address reproduction circuit 1 reads an address in the ID in thereproduced signal 100 by the recording/reproduction light beam 23 andproduces the address detection signal 103, address data 108 and addressodd/even signal 106. The address data 108 and address detection signal103 are applied to the sector control circuit 8. The sector controlcircuit 8 supplies the erasing gate signal 110 to the erasing laserdrive circuit 13 and the modulation start signal 111 to the datamodulation circuit 14 in accordance with the erasing/recording commandindicated by the command signals 109.

The data modulation circuit 14 supplies the write data 114 and the writegate signal 113 to the recording/reproduction laser drive circuit 15 andthe AND gate 12, respectively.

The differentiation circuit 10 detects a rising edge of the erasing gatesignal 110 to set the flip-flop 11, which validates the erasing laserdrive circuit enabling signal 112. Consequently, the erasing laser drivecircuit 13 operates to turn on the erasing laser source 16 and causes itto start an erasing operation as shown in FIG. 4(m). As a result, thesignal 101 shown in FIG. 4(e) is produced by an erasing light beamemitted from the erasing laser source 16.

The address detection signal 103 is supplied to the M1 gate signalgeneration circuit 2 and M2 gate signal generation circuit 3, whichcircuits 2 and 3 produce an M1 gate signal 104 and an M2 gate signal 105shown in FIG. 4(h) and FIG. 4(i), respectively. The M1 gate signal 104and the M2 gate signal 105 operate to detect that the erasing light beam24 is positioned on an even-numbered track or an odd-numbered track byseparating in time the mark signals M1 and M2 in the reproduced signal101 by the erasing light beam 24.

The signal 101 shown in FIG. 4(e) reproduced from the optical disk bythe erasing light beam 24 having a beam spot in the shape of anelongated ellipse has an inferior resolution as compared with that ofthe signal shown in FIG. 4(d) reproduced by the recording/reproductionlight beam 23, so that it cannot reproduce the ID. However, it cansatisfactorily reproduce the mark signals M1 and M2 formed as a land ora groove of several μm such as shown in FIGS. 2A to 2C. The reproducedsignal 101 by the erasing light beam 24 is converted through thecomparator 9 into a binary signal 102 at a predetermined thresholdvalue, and the resulting binary reproduced signal 102 is supplied to theAND gates 5 and 6.

The address odd/even signal 106 is applied straightly to the AND gate 6,while, it is inverted through the inverter 4 and applied to the AND gate5. The AND gates 5 and 6 and a NOR gate 7 in combination operate toselect the mark signal M1 or M2 in the binary reproduced signal 102. Theaddress odd/even signal 106 presently indicates an odd track, andtherefore the AND gate 6 is selected, and the tracking deviationdetection signal 107 corresponding to the mark signal M2 is produced asshown in FIG. 4(j). The tracking deviation detection signal 107 resetsthe flip-flop 11 thereby to invalidate the erasing laser drive circuitenabling signal 112. Consequently, the erasing laser source 16 is turnedoff as shown in FIG. 4(m). The data recording operation is alsointerrupted by blocking a write gate signal 113 through the AND gate 12.

The signal waveforms appearing when the recording/reproduction lightbeam 23 is positioned on an even-numbered track is shown by the brokenlines in FIG. 4, and they are identical with those in theabove-mentioned case except that the AND gate 5 is selected by theaddress odd/even signal 106 thereby to detect the mark signal M1.

According to this embodiment, as described above, the mark signal M1 orM2 immediately behind the ID is identified depending on the odd or evennumber of the address of the track at the timing of generation of the M1or M2 gate signal caused by the address detection signal 103, which isoutputted from the address reproduction circuit 1, whereby erroneouserasing and recording can be prevented even when ±1 track deviation ofthe erasing light beam from the recording/reproduction light beamoccurs.

FIG. 5 is a block diagram showing a second embodiment of the opticalinformation recording/reproduction apparatus using the optical disk ofthe present invention. In the figure, circuit blocks and signalsidentical with those shown in FIG. 3 are denoted by the same referencenumerals and symbols. In FIG. 5, indicated by 18 is an inverter, 19 isan OR gate, and 115 is an erasing light beam in-track detection signalindicating that the erasing light beam 24 is positioned on the sametrack with the recording/reproduction light beam 23.

The following describes the operation of the optical informationrecording/reproduction apparatus according to the second embodiment ofthis invention having the construction as described above. Theexplanation is based on the assumption that the erasing light beam 24 ispositioned on the same odd address track with the recording/reproductionlight beam 23.

The address reproduction circuit 1 reads an address in the ID in thereproduced signal 100 by the recording/reproduction light beam 23 andproduces an address detection signal 103 and an address odd/even signal106. The address detection signal 103 is applied to the M1 gategeneration circuit 2 and the M2 gate generation circuit 3, whichcircuits 2 and 3 produce an M1 gate signal 104 and an M2 gate signal105, respectively.

The reproduced signal 101 by the erasing light beam 24 reproduces a marksignal M1. The reproduced signal 101 is converted through the comparator9 into a binary signal 102 at a predetermined threshold value, and it issupplied to the AND gates 5 and 6 as a binary reproduced signal 102 bythe erasing light beam 24. The address odd/even signal 106 becomes ahigh level, which causes the AND gate 5 and the OR gate 19 to producethe mark signal M1 of the binary reproduced signal 102 by the erasinglight beam 24 as an erasing light beam in-track detection signal 115. Onthe other hand, when the erasing light beam 24 is positioned on the sameeven address track with the recording/reproduction light beam 23, theaddress odd/even signal 106 is a low level, and then it is invertedthrough the inverter 18, which inverted signal causes the AND gate 6 andthe OR gate 19 to produce the mark signal M2 of the binary reproducedsignal 102 by the erasing light beam 24 as an erasing light beamin-track detection signal 115.

Next, an explanation will be given of the operation of the apparatus ofthe present invention in which the erasing light beam 24 is positionedon a track deviated by ±1 track from a track on which therecording/reproduction light beam 23 is positioned. The reproducedsignal 101 by the light erasing beam 24 produces a mark signal M2 whenthe recording/reproduction light beam 23 is positioned on an odd addresstrack, while, it produces a mark signal M1 when therecording/reproduction light beam 23 is positioned on an even addresstrack. Therefore, the AND gates 5 and 6 operate to block the binaryreproduced signal 102 by the erasing light beam 24 in any case, and, asa result, an erasing light beam in-track detection signal 115 is notdetected. Thus, by monitoring the erasing light beam in-track detectionsignal 115 with a CPU or the like, it is possible to detect thecoexistence of the erasing light beam 24 and the recording/reproductionlight beam 23 on the same track.

As described above, according to this embodiment, it is possible toconfirm that the erasing light beam 24 and the recording/reproductionlight beam 23 are positioned on the same track, by identifying the marksignal M1 or M2 immediately behind the ID depending on the odd or evennumber of the address of the track at the timing of generation of the M1or M2 gate signal caused by the address detection signal 103, which isoutputted from the address reproduction circuit 1.

FIG. 6 is a block diagram showing a third embodiment of the opticalinformation recording/reproduction apparatus of the present invention.In the figure, reference numerals 1, 16, 100, 101, 103, 106 and 110denote the same constitutional elements and signals shown in FIG. 3.Indicated by 20 is a mark signal detection circuit, 21 is a D-input typeflip-flop, 22 is an erasing laser drive circuit, 16 is an erasing lasersource, 116 is a mark signal detection signal, and 117 is an outputsignal from the D-FF 21.

FIG. 7 shows signal waveforms appearing at various portions of theoptical information recording/reproduction apparatus shown in FIG. 6 forexplaining the operation thereof. FIGS. 7(a) and 7(b) show reproducedsignals 100 reproduced from ar odd address track and an even addresstrack by the recording/reproduction light beam 23, respectively. FIG.7(c) shows a reproduced signal 101 reproduced by the erasing light beam24. FIG. 7(d) shows an erasing gate signal 110, FIG. 7(c) a mark signaldetection signal 116, FIG. 7(f) an output signal 117 from the D-FF 21,and FIG. 7(g) an erasing light beam output signal 24 from the erasinglaser source 16.

The following explains the operation of the optical informationrecording/reproduction apparatus of the third embodiment of the presentinvention having the construction as described above.

As an example, the following explanation assumes a case where therecording/reproduction light beam 23 is positioned on an odd addresstrack as shown in FIG. 7(a).

The erasing laser source 16 is operating continuously at a reproductionpower level. When the erasing light beam 24 is positioned on an oddaddress track on the optical disk, the reproduced signal 101 reproducedfrom the odd address track by the erasing light beam 24 is applied tothe mark signal detection circuit 20, which then outputs a mark signalM1 as the mark signal detection signal 116.

The mark signal detection signal 116 operates to latch the erasing gatesignal 110 in the D-FF 21 to actuate the erasing laser drive circuit 22,which then supplies an erasing power output current to the erasing lasersource 16 to cause it to produce a laser beam of the erasing power levelso that the data field DF is erased over the period shown in FIG. 7(g).

If the erasing light beam 24 is positioned on an even address track asshown by the broken line waveform in FIG. 7(c), the reproduced signal101 reproduced by the erasing light beam 24 reproduces the mark signalM2, and therefore the mark signal detection circuit 20 does not producethe mark signal detection signal 116. Accordingly, the erasing laserdrive circuit 22 is not actuated to produce an erasing power leveloutput signal, even if the erasing gate signal 110 is applied to theD-FF 21. Thus, erroneous erasing of the even address track can beprevented.

According to this third embodiment, the mark signal M1 or M2 immediatelybehind the ID is respectively identified depending on an odd or evenaddress of the track, at the timing of generation of the M1 or M2 gatesignal caused by the address detection signal 103 which is outputtedfrom the address reproduction circuit 1, whereby it becomes possible toprevent erroneous erasing or recording which occurs when the tracking ofthe erasing light beam 24 deviates by ±1 track from that of therecording/reproduction light beam 23. It is of course possible to usethe mark signals M1 and M2 of this embodiment as a mirror section sothat it is used commonly with the TOF (tracking offset detection flag)for correcting an inclination of the optical disk.

As described above, the present invention has a great practicaladvantage of being capable of detecting the tracking deviation of theerasing light beam and preventing erroneous erasing caused by thetracking deviation.

We claim:
 1. An optical disk having a series of adjacent tracks each ofsaid tracks being divided into a plurality of sectors, the optical diskbeing adapted to have information erased, recorded and reproduced on asector basis by using an erasing light beam and a succeedingrecording/reproduction light beam, each of said sectors comprising: (a)a sector identifier containing address information of said sector; (b) adata field in which information is recorded; and (c) a mark signalcomprising one of a first kind of long mark signal and a second kind oflong mark signal, even ones of said adjacent tracks having said firstkind of long mark signal recorded therein and odd ones of said adjacenttracks having said second kind of long mark signal recorded therein,said mark signal being disposed between said sector identifier and saiddata field to follow said sector identifier at a first distance in oneof said even tracks and a second distance in one of said odd tracks,whereby said mark signal is readable by said erasing light beam todiscriminate whether the erasing light beam is positioned on an adjacenttrack relative to a track on which the recording/reproduction light beamis positioned on said optical disk.
 2. An optical disk according toclaim 1 wherein said mark signal is one of two kinds of mark signalspositioned with respective different distances from said sectoridentifier depending on whether the track address designates one of saideven tracks or said odd tracks.
 3. An optical disk according to claim 1wherein said mark signal is of a uniform phase construction differentfrom the track structure of said data field.
 4. An optical diskaccording to claim 2 wherein each of said two kinds of mark signals areof a uniform phase construction different from the track structure ofsaid data field.
 5. An optical disk according to claim 3 wherein saidmark signal is formed in the shape of a land when said data field isformed in the shape of a groove.
 6. An optical disk according to claim 4wherein each of said two kinds of mark signals are formed in the shapeof a land when said data field is formed in the shape of a groove.
 7. Anoptical disk according to claim 3 wherein said mark signal is formed inthe shape of a groove when said data field is formed in the shape of aland.
 8. An optical disk according to claim 4 wherein each of said twokinds of mark signals are formed in the shape of a groove when said datais formed in the shape of a land.